Jing-Chun Tang

Characteristics of biochar and its application in remediation of contaminated soil

Biochar is produced by thermal decomposition of biomass under oxygen-limited conditions (pyrolysis), and it has received attention in soil remediation and waste disposal in recent years. The characteristics of biochar are influenced mainly by the preparation temperature and biomass. Higher pyrolysis temperature often results in the increased surface area and carbonized fraction of biochar leading to high sorption capability for pollutants. Biochars derived from various source materials show different properties of surface area, porosity and the amount of functional groups which are important concerning on the effect of biochar. Biochar has been proved to be effective in improving soil properties and increasing crop biomass. It has also been suggested that it can even enhance crop resistance to disease. Biochar has recently been used to remediate soil with both heavy metal and organic pollutants. The mechanism is electrostatic interaction and precipitation in the case of heavy metal, and the surface adsorption, partition and sequestration in the case of organic contaminants. However, application of biochar in soil has been shown to result in decreased efficacy of pesticides, which indicates a trade-off between the potentially promising effect of biochar on pesticide remediation and its negative effect on pesticide efficacy. While arguments on the effectiveness of biochar appear sound, further research is needed prior to widespread application of biochar in soil remediation.

Chemical and microbial properties of various compost products

Abstract Chemical and microbial characterizations were carried out for forty-four compost products, whose raw materials were classified into seven categories: wood, coffee ground, grass, buckwheat shells, animal manure, food waste, and others. Microbial community structure in the composts was examined by quinone profile analysis. Values of the chemical and microbial properties varied considerably as follows: moisture content 3.1–82.7%, pH 4.38–9.44, electric conductivity (EC) 0.12–17.08 mS cm−1, total carbon (TC) content 16.9–51.0%, total nitrogen (TN) content 0.61–9.83%, C / N ratio 5.2–53.1, ash content 4.2–63.2%, total quinone (TQ) content 0.0–215.2 µmol kg−1 dry sample, and value of quinone diversity (DQ) index 0.0–20.8. The wide range in the values expressed the diversity of the chemical and microbial properties of various compost products. The chemical properties were related to the raw materials while the microbial properties tended to be less related. Total menaquinone contents were higher than the total ubiquinone contents in most of the composts. The common major quinone species was menaquinone-7, indicating the predominance of Bacillus. The average mole fractions of menaquinones with partially saturated and long side-chains accounted for about 37% of the TQ content, indicating the proliferation of Actinobacteria. Multiple regression analysis suggested that microbial properties were significantly related to the moisture content, pH, and C / N ratio of the compost products. The DQ increased with the increase of the quinone contents and became stable at the value of about 16.5 in the composts with more than 50 nmol kg−1 of quinones. At the same time these values were observed only in the composts with C / N ratios lower than 20.